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WIP describing the jit stuff

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Spencer Tipping 2017-03-09 19:48:17 -07:00
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117
README.md
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@ -163,3 +163,120 @@ user 0m1.328s
sys 0m0.000s sys 0m0.000s
$ $
``` ```
### JIT design
The basic strategy is to replace `interpret(registers, code)` with a function
`compile(code)` that returns a pointer to a function whose signature is this:
`void compiled(registers*)`. The memory for the function needs to be allocated
using `mmap` so we can set permission for the processor to execute it.
The easiest way to start with something like this is probably to emit the
assembly for `simple.c` to see how it works:
```sh
$ gcc -S simple.c
```
Edited/annotated highlights from the assembly `simple.s` (whose floating-point
code is a little circuitous):
```s
interpret:
pushq %rbp
movq %rsp, %rbp // standard x86-64 function header
subq $48, %rsp // allocate space for local variables
movq %rdi, -40(%rbp) // callee saves %rsi and %rdi
movq %rsi, -48(%rbp)
jmp for_loop_condition
for_loop_body:
<a bunch of stuff>
cmpl $43, %eax // case '+'
je add_branch
cmpl $61, %eax // case '='
je assign_branch
cmpl $42, %eax // case '*'
je mult_branch
jmp switch_default // default
assign_branch:
// the "bunch of stuff" above calculated *src and *dst, which are
// stored in -24(%rbp) and -32(%rbp).
movq -24(%rbp), %rax // %rax = src
movsd (%rax), %xmm0 // %xmm0 = src.r
movq -32(%rbp), %rax // %rax = dst
movsd %xmm0, (%rax) // dst.r = %xmm0
movq -24(%rbp), %rax // %rax = src
movsd 8(%rax), %xmm0 // %xmm0 = src.i
movq -32(%rbp), %rax // %rax = dst
movsd %xmm0, 8(%rax) // dst.i = %xmm0
jmp for_loop_step
add_branch:
movq -32(%rbp), %rax // %rax = dst
movsd (%rax), %xmm1 // %xmm1 = dst.r
movq -24(%rbp), %rax // %rax = src
movsd (%rax), %xmm0 // %xmm0 = src.r
addsd %xmm1, %xmm0 // %xmm0 += %xmm1
movq -32(%rbp), %rax // %rax = dst
movsd %xmm0, (%rax) // dst.r = %xmm0
movq -32(%rbp), %rax // same thing for src.i and dst.i
movsd 8(%rax), %xmm1
movq -24(%rbp), %rax
movsd 8(%rax), %xmm0
addsd %xmm1, %xmm0
movq -32(%rbp), %rax
movsd %xmm0, 8(%rax)
jmp for_loop_step
mult_branch:
movq -32(%rbp), %rax
movsd (%rax), %xmm1
movq -24(%rbp), %rax
movsd (%rax), %xmm0
mulsd %xmm1, %xmm0
movq -32(%rbp), %rax
movsd 8(%rax), %xmm2
movq -24(%rbp), %rax
movsd 8(%rax), %xmm1
mulsd %xmm2, %xmm1
subsd %xmm1, %xmm0
movsd %xmm0, -16(%rbp) // double r = src.r*dst.r - src.i*dst.i
movq -32(%rbp), %rax
movsd (%rax), %xmm1
movq -24(%rbp), %rax
movsd 8(%rax), %xmm0
mulsd %xmm0, %xmm1
movq -32(%rbp), %rax
movsd 8(%rax), %xmm2
movq -24(%rbp), %rax
movsd (%rax), %xmm0
mulsd %xmm2, %xmm0
addsd %xmm1, %xmm0
movsd %xmm0, -8(%rbp) // double i = src.r*dst.i + src.i*dst.r
movq -32(%rbp), %rax
movsd -16(%rbp), %xmm0
movsd %xmm0, (%rax) // dst.r = r
movq -32(%rbp), %rax
movsd -8(%rbp), %xmm0
movsd %xmm0, 8(%rax) // dst.i = i
jmp for_loop_step
for_loop_step:
addq $3, -48(%rbp)
for_loop_condition:
movq -48(%rbp), %rax
movzbl (%rax), %eax
testb %al, %al
jne .L8
nop
leave // reset %rsp
ret // pop and jmp
```

293
simple.s Normal file
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@ -0,0 +1,293 @@
.file "simple.c"
.section .rodata
.align 8
.LC0:
.string "undefined instruction %s (ASCII %x)\n"
.text
.globl interpret
.type interpret, @function
interpret:
.LFB2:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
subq $48, %rsp
movq %rdi, -40(%rbp)
movq %rsi, -48(%rbp)
jmp .L2
.L8:
movq -48(%rbp), %rax
addq $2, %rax
movzbl (%rax), %eax
movsbq %al, %rax
salq $4, %rax
leaq -1552(%rax), %rdx
movq -40(%rbp), %rax
addq %rdx, %rax
movq %rax, -32(%rbp)
movq -48(%rbp), %rax
addq $1, %rax
movzbl (%rax), %eax
movsbq %al, %rax
salq $4, %rax
leaq -1552(%rax), %rdx
movq -40(%rbp), %rax
addq %rdx, %rax
movq %rax, -24(%rbp)
movq -48(%rbp), %rax
movzbl (%rax), %eax
movsbl %al, %eax
cmpl $43, %eax
je .L4
cmpl $61, %eax
je .L5
cmpl $42, %eax
je .L6
jmp .L9
.L5:
movq -24(%rbp), %rax
movsd (%rax), %xmm0
movq -32(%rbp), %rax
movsd %xmm0, (%rax)
movq -24(%rbp), %rax
movsd 8(%rax), %xmm0
movq -32(%rbp), %rax
movsd %xmm0, 8(%rax)
jmp .L7
.L4:
movq -32(%rbp), %rax
movsd (%rax), %xmm1
movq -24(%rbp), %rax
movsd (%rax), %xmm0
addsd %xmm1, %xmm0
movq -32(%rbp), %rax
movsd %xmm0, (%rax)
movq -32(%rbp), %rax
movsd 8(%rax), %xmm1
movq -24(%rbp), %rax
movsd 8(%rax), %xmm0
addsd %xmm1, %xmm0
movq -32(%rbp), %rax
movsd %xmm0, 8(%rax)
jmp .L7
.L6:
movq -32(%rbp), %rax
movsd (%rax), %xmm1
movq -24(%rbp), %rax
movsd (%rax), %xmm0
mulsd %xmm1, %xmm0
movq -32(%rbp), %rax
movsd 8(%rax), %xmm2
movq -24(%rbp), %rax
movsd 8(%rax), %xmm1
mulsd %xmm2, %xmm1
subsd %xmm1, %xmm0
movsd %xmm0, -16(%rbp)
movq -32(%rbp), %rax
movsd (%rax), %xmm1
movq -24(%rbp), %rax
movsd 8(%rax), %xmm0
mulsd %xmm0, %xmm1
movq -32(%rbp), %rax
movsd 8(%rax), %xmm2
movq -24(%rbp), %rax
movsd (%rax), %xmm0
mulsd %xmm2, %xmm0
addsd %xmm1, %xmm0
movsd %xmm0, -8(%rbp)
movq -32(%rbp), %rax
movsd -16(%rbp), %xmm0
movsd %xmm0, (%rax)
movq -32(%rbp), %rax
movsd -8(%rbp), %xmm0
movsd %xmm0, 8(%rax)
jmp .L7
.L9:
movq -48(%rbp), %rax
movzbl (%rax), %eax
movsbl %al, %ecx
movq stderr(%rip), %rax
movq -48(%rbp), %rdx
movl $.LC0, %esi
movq %rax, %rdi
movl $0, %eax
call fprintf
movl $1, %edi
call exit
.L7:
addq $3, -48(%rbp)
.L2:
movq -48(%rbp), %rax
movzbl (%rax), %eax
testb %al, %al
jne .L8
nop
leave
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE2:
.size interpret, .-interpret
.section .rodata
.LC1:
.string "P5\n%d %d\n%d\n"
.text
.globl main
.type main, @function
main:
.LFB3:
.cfi_startproc
pushq %rbp
.cfi_def_cfa_offset 16
.cfi_offset 6, -16
movq %rsp, %rbp
.cfi_def_cfa_register 6
subq $1712, %rsp
movl %edi, -1700(%rbp)
movq %rsi, -1712(%rbp)
movq %fs:40, %rax
movq %rax, -8(%rbp)
xorl %eax, %eax
movl $255, %ecx
movl $900, %edx
movl $1600, %esi
movl $.LC1, %edi
movl $0, %eax
call printf
movl $0, -1684(%rbp)
jmp .L11
.L19:
movl $0, -1688(%rbp)
jmp .L12
.L18:
pxor %xmm0, %xmm0
cvtsi2sd -1688(%rbp), %xmm0
movsd .LC2(%rip), %xmm1
divsd %xmm1, %xmm0
movsd .LC3(%rip), %xmm1
subsd %xmm1, %xmm0
movsd .LC4(%rip), %xmm1
mulsd %xmm1, %xmm0
movsd %xmm0, -1680(%rbp)
pxor %xmm0, %xmm0
cvtsi2sd -1684(%rbp), %xmm0
movsd .LC5(%rip), %xmm1
divsd %xmm1, %xmm0
movsd .LC3(%rip), %xmm1
subsd %xmm1, %xmm0
movsd .LC6(%rip), %xmm1
mulsd %xmm1, %xmm0
movsd %xmm0, -1672(%rbp)
movl $1, -1692(%rbp)
jmp .L13
.L14:
movl -1692(%rbp), %eax
cltq
salq $4, %rax
addq %rbp, %rax
subq $1672, %rax
pxor %xmm0, %xmm0
movsd %xmm0, (%rax)
movl -1692(%rbp), %eax
cltq
salq $4, %rax
addq %rbp, %rax
subq $1672, %rax
movsd (%rax), %xmm0
movl -1692(%rbp), %eax
cltq
salq $4, %rax
addq %rbp, %rax
subq $1680, %rax
movsd %xmm0, (%rax)
addl $1, -1692(%rbp)
.L13:
cmpl $3, -1692(%rbp)
jle .L14
movl $0, -1692(%rbp)
jmp .L15
.L17:
movq -1712(%rbp), %rax
addq $8, %rax
movq (%rax), %rdx
leaq -1680(%rbp), %rax
movq %rdx, %rsi
movq %rax, %rdi
call interpret
addl $1, -1692(%rbp)
.L15:
cmpl $255, -1692(%rbp)
jg .L16
movsd -1664(%rbp), %xmm1
movsd -1664(%rbp), %xmm0
mulsd %xmm0, %xmm1
movsd -1656(%rbp), %xmm2
movsd -1656(%rbp), %xmm0
mulsd %xmm2, %xmm0
addsd %xmm1, %xmm0
movsd .LC8(%rip), %xmm1
ucomisd %xmm0, %xmm1
ja .L17
.L16:
movl -1692(%rbp), %eax
movl %eax, %edx
movl -1688(%rbp), %eax
cltq
movb %dl, -1616(%rbp,%rax)
addl $1, -1688(%rbp)
.L12:
cmpl $1599, -1688(%rbp)
jle .L18
movq stdout(%rip), %rdx
leaq -1616(%rbp), %rax
movq %rdx, %rcx
movl $1600, %edx
movl $1, %esi
movq %rax, %rdi
call fwrite
addl $1, -1684(%rbp)
.L11:
cmpl $899, -1684(%rbp)
jle .L19
movl $0, %eax
movq -8(%rbp), %rcx
xorq %fs:40, %rcx
je .L21
call __stack_chk_fail
.L21:
leave
.cfi_def_cfa 7, 8
ret
.cfi_endproc
.LFE3:
.size main, .-main
.section .rodata
.align 8
.LC2:
.long 0
.long 1083768832
.align 8
.LC3:
.long 0
.long 1071644672
.align 8
.LC4:
.long 2576980378
.long 1074370969
.align 8
.LC5:
.long 0
.long 1082925056
.align 8
.LC6:
.long 3435973837
.long 1073532108
.align 8
.LC8:
.long 0
.long 1074790400
.ident "GCC: (Ubuntu 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609"
.section .note.GNU-stack,"",@progbits